Boris Johnson has described Ukip voters as peasants in revolt after Eurosceptic parties swept to victory across the union.

The London mayor painted a scene of "pitchfork-wielding populists" converging on Brussels "drunk on local hooch and chanting nationalist slogans and preparing to give the federalist machinery a good old kicking with their authentically folkloric clogs".

Writing in the Telegraph, he compared Eurosceptic parties, including Ukip, Dutch rightwing firebrands and Greek anti-capitalists, to people taking part in "a kind of peasants' revolt" or a "jacquerie" – a bloody uprising against the French nobility in 1358.

However, Johnson concluded that this would be a boost for David Cameron, despite the Conservatives having come third in a national election for the first time.

Casting the results in a positive light for the Tories, he insisted that it would help the prime minister in his attempts to renegotiate with the European Union as Brussels would not be able to ignore the "vulgar expressions of democratic feeling".

"This European election is an expression of revulsion and discontent and it is a mandate for reform," he said. "Across the EU, mainstream politicians like Nicolas Sarkozy are now saying what we Conservatives have been saying for years: that the EU needs to do less, to cost less, and to be less intrusive in the way it does it. There is only one government in Europe that has been campaigning solidly for the renegotiation that is needed, and that is David Cameron and the Conservative-led coalition."

He said it would not be good enough "just to circle the wagons and tell the people of Europe to get stuffed, because next time the frustration of the electorate may be uncontainable", adding that the message of the people to the EU was "changer ou mourir!" – to change or die.

His stance was echoed by Cameron who said the message that people are disillusioned with the EU was "received and understood".

He told BBC Radio 4's Today programme that he was confident the Conservatives could secure a "good renegotiation" on the European Union before a referendum that the party has promised to hold before the end of 2017.